Through the windows of Brookfield Zoo’s perching bird house, visitors can watch some of the last Guam kingfishers in the world and ponder a mystery that has stumped some of the most prominent bird experts for two decades: Why doesn’t the kingfisher thrive in captivity?
The birds, from the remote Pacific Island of Guam, were preyed upon for decades by brown tree snakes accidentally brought to Guam on ships hauling in scrap metal from Pacific battlegrounds at the end of World War II.
In 1985, American zoos removed the last 29 wild kingfishers from Guam, hoping a captive breeding program would revive the species and allow it to be reintroduced.
But that has not happened, even though American zoos in recent years have expended an inordinate amount of time, research and money trying to save the bird–a colorful, big-beaked blue jay-size cousin to the Australian kookaburra.
On Sunday, 40 research biologists, nutritionists, geneticists and bird keepers from zoos, universities and research stations around the U.S. and western Pacific wrapped up a three-day workshop at Brookfield–home to 13 of the 50 to 60 Guam kingfishers left.
“It’s probably one of the most critically endangered species in the world,” said Beth Bahner of the Philadelphia Zoo and head of the American Zoo and Aquarium Association’s species survival plan for Guam kingfishers. “Definitely it is one of the most difficult animals to care for in captivity.”
Scientists say the captive females often show no interest in mating with males that keepers pair up with them. When they do mate, an inordinate number of offspring die young, without leaving a succeeding generation.
“The problem is we never had a chance to study them in the wild in Guam before we had to go in there and rescue them from the snakes,” Bahner said.
“We don’t know what exactly they ate in the wild. We don’t know exactly what sorts of materials they prefer in nature for building nests.
“We keep losing them in the 2- to 5-year-old range, so that we’re not seeing them get through what should be a normal 17- to 20-year life cycle.”
Bahner coordinates research on the birds, polices the husbandry standards of the 11 zoos keeping the birds and determines which birds should be mated to avoid inbreeding.
“There seems to be no big pattern or rhyme or reason for the early mortality of so many of our birds,” Bahner said. “My suspicion is there is something lacking in their nutrition.
“We feed them properly and get them going early in life, but there must something missing in the diet we give them so that, as young adults, their immunity situation is leaving them unprotected, or causing a stress we don’t yet see.”
The best that naturalists can determine is that the natural diet of the wild kingfishers was primarily small lizards, insects and occasional small mammals and birds.
Zookeepers first based the diets they fed to the 29 rescued birds on anoles, small green lizards common to Florida, purchased from suppliers who catch them in the wild.
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The birds at first thrived. By 1991 their number grew to 65, but in 1991 a killer freeze descended on the American south, temporarily disrupting the birds’ major food source. The zoos then had to scramble to devise new diets, but soon began to see their young adult birds die off, wiping out population gains.
“Without knowing their diet on Guam, we’ve had to make some educated guesses about their nutritional needs by looking at domestic animals roughly their size,” said Sue Crissey, Brookfield’s director of nutritional services.
“The closest to them is the chicken, but kingfishers are meat and insect eaters, and chickens aren’t. So we also look at the diets of house cats for some clues.”
When the anole supply ran out in 1991, Crissey said, zoos substituted “pinkies,” hairless baby mice, rounded out by servings of crickets, mealworms and waxworms.
Keepers soon noticed that the birds had calcium deficits on the mice diet. They countered that by feeding the insects and worms exclusive calcium diets several days before they in turn were fed to the birds.
“We give them both lizards and pinkies now,” Crissey said.
“We’ve even been trying out commercial cat food with the birds, but that only goes so far. Food is part of the courting ritual for the birds, with males bringing offerings of lizards in their beaks to the females, and cat food just doesn’t seem to take the place of that.”
The Guam kingfisher is a subspecies of the Micronesian kingfisher. Another subspecies that had populated Japan’s Ryuku islands went extinct about 1890, but two other subspecies hang on tenuously in what remains of the wild on two other Pacific islands: Palau and Pohnpei.
Looking for clues to how wild Guam kingfishers lived, zoo and conservation organizations are sponsoring a three-year study of the subspecies on Pohnpei, a volcanic mountain island 1,200 miles southeast of Guam.
“The kingfishers on Pohnpei fill the same niche in nature that blue jays fill in the American Midwest,” said Dylan Kesler, an Oregon State University graduate student who has completed two of the three years of observations on Pohnpei.
“Like jays they perch on phone wires, eat all sorts of things and are noisy, with a sort of guttural haw-haw-haw call a little like a crow’s.”
Although he is years away from finishing the analysis of his data, at the Brookfield meeting Kesler used some preliminary findings to suggest how keepers might inveigle female kingfishers to mate more enthusiastically.
He likened the wild Pohnpei kingfisher females to opportunistic gold diggers that are attracted to sugar daddy males presiding over territories rich with nesting material and food but are dismissive of less well-off males.
“The females seem to select males for what the males have, not for what they are,” he said. “When they visit the territories of potential male mates, they seem most convinced by those with an abundance of potential nest sites and lots of available food.
“I’ve seen almost immediate mating behavior take place when the female has looked around and seen a wealth of nesting options and food in the male’s territory.
“I am suggesting to zoos that instead of just putting out one or two tree trunks for nesting when they pair off a male and a female, they might try putting many tree trunks in the habitat.”
While Kesler’s mission was to find information that might help the Guam kingfisher survive, he has also discovered a disastrous drop in kingfisher populations on Palau and Pohnpei. Their numbers have fallen by 60 percent or more in the last two decades, he said, both cases apparently due to human intrusion.
In Palua, the culprits seem to be Japanese resort developers who cut down most of the island’s–and the kingfisher’s–forested areas to make way for golf courses that never were built after the recent Asian monetary crisis.
On Pohnpei, the suspected villains are small, poisonous toads that sugar cane growers have been importing to protect their fields from certain pests. Often fatally toxic to animals that eat them, Kesler believes the cane toads may be killing Pohnpei’s kingfishers.
“If we’re not careful,” said Kesler, “we may find ourselves doing a rescue operation on Pohnpei like the one on Guam, instead of going there to study the birds in nature.”